Aumento significativo de la resistencia a fosfomicina en cepas de Escherichia coli productoras de ß-lactamasas de espectro extendido (BLEE) aisladas de urocultivos (2005-2009-2011)

Introduction. Escherichia coli is the most important uropathogen. The appearance of extended- spectrum beta-lactamase (ESBL)-producing E.coli in urinary tract infections (UTI) constitutes an important therapeutic challenge that requires the study of its evolution throughout time in order to establish a suitable empirical treatment. Our aim was to determine the prevalence of ESBL-producing E. coli urinary isolates in 2005, 2009 and 2011. We also determined the antimicrobial coresistance to several agents, including fosfomycin. Methods. We analyzed 5053, 6324 and 6644 E. coli isolates obtained from urine cultures in 2005, 2009 and 2011 respectively. Duplicate isolates were excluded. Antimicrobial susceptibility was determined by the Wider microdilution system (Soria Melguizo S.A.) and the phenotypic pattern of resistance that indicated a BLEE-producing E.coli was selected (CLSI 2009). Results. 3.9% of strains (198) were ESBL producers in 2005, 7.3% (463) in 2009 and 8.7% (584) in 2011. Resistance to carbapenems was detected in 2009, they inhibited more than the 95% of strains in 2011. Among the non-beta-lactams, colistin was the most active antibiotic followed by nitrofurantoin. Ciprofloxacin and sulfamethoxazole-trimethoprim were not effective with 80% and 60% resistant isolates, respectively. An increasing resistance trend, from 0% to 9.3% in 2009 and 14.4% in 2011 was observed for fosfomycin. Conclusions. From 2005 our institution had an increasing prevalence of ESBL-producing E. coli rising to 8.7% in 2011. Carbapenems are still the most active agents. The increase of resistance was significant for fosfomycin.